Variable transformer pick-off



May 16, 1950 F. P. STROTHER Er AL VARIABLE TRANSFORMER PICKOFF 2 Sheets-Sheet 1 Filed Sept. 24, 1945 M g w i FF 1 W 1% w! M! a A L I Q M w L LJ g D R/ f M w 1L frecl P 3trother Bert A. C055 7 May 16, 1950 F. P. STROTHER El AL 2,507,335

VARIABLE TRANSFORMER PICKOFF Filed Sept. 24, 1945 2 Sheets-Sheet 2 Vii;

Bert A. Cass Patented May 16, 1950 UNITED STATES PATENT OFFICE VARIABLE TRANSFORMER PICK-OFF Fred P. Strother, Minneapolis, and Bert A. 0055,

St. Louis Park, Minn., assignors to Minneapolis- Honeywell Regulator Company, Minneapolis, Minn., a corporation of Delaware Application September 24, 1945, Serial No. 618,180

4 Claims. 1

Our invention relates to variable transformer pickoffs and particularly to transformer pickoifs or control devices in which a feeble actuating force is utilized to produce an amplified controlling force or electric current.

Another object of the invention resides in providing a pickofi in which a substantial signal may be had at the vicinity of the zero setting of the actuating member.

A still further object of the invention resides in providing a pickoff using a magnetic circuit and in which the reluctance of the magnetic circuit remains substantially constant throughout the entire range of operation of the device.

Another object of the invention resides in providing a pickofi in which no appreciable counter magneto motive force is produced to load the device.

A feature of the invention resides in providing a device in which the movement of the movable actuating member is damped so as to quickly bring the actuating member back to rest.

An object of the invention resides in providing a pickoff including a coil having a core of nonmagnetizable material and a core structure having two air gaps traversed by opposite magnetic fields at certain instants and in arranging the coil so that the flux from both of the poles passes through the core of the coil and in further mounting the coil for movement so that the proportion of the fluxes intercepted varies in accordance with the position of the coil relative to the poles.

Another object of the invention resides in providing a pickoff having a magnetic circuit including a core formed with an air gap and in further providing a coil movable in said air gap and having its inside dimension in the direction of its movement equal to the corresponding dimension of the core at the air gap.

A feature of the invention resides in constructing the dimensions of the core of the coil in the direction of movement thereof substantially equal to the distance between the outermost edges of said pole faces in the same direction.

Other objects of the invention reside in the novel combination and arrangement of parts and in the details of construction hereinafter illustrated and/or described.

In the drawings:

Fig. l is a wiring diagram of an electric control system illustrating an embodiment of our invention.

Fig. 2 is a longitudinal elevational section view of the control device utilized with the system disclosed in Fig. 1.

Fig. 3 is a plan sectional view taken on line 33 of Fig. 2.

Fig. 4 is an elevational sectional view taken on line 4-4 of Fig. 2.

Fig. 5 is a wiring diagram of the damping device of the invention.

The variable transformer pickoif or control device shown in Figs. 2, 3 and 4 comprises a frame it formed of heavy metal which is bent to provide a base H and spaced uprights l2 and I3. The upright l3 has a flange l4 extending outwardly therefrom which serves a purpose to be presently more fully described.

Attached to the upper end of the upright 12 is a tubular housing l5 which has a bore [6 therein. In this bore are mounted two ball bearings l! and I 8 which rotatably support a shaft 19. The movable actuating member of the device which is designated by the reference numeral 39 is carried by the shaft l9. This actuating member comprises a hanger 20 which is attached to said shaft at the end thereof located between the uprights I2 and E3. The hanger 20 has attached to the lower end thereof by means of screws 22 an insulating mounting 2|. The mounting 2! is formed with a rectangular opening 23 in which is mounted a coil 26 of suitable insulated wire. The ends of this coil are connected by means of suitable pigtails not shown with binding posts or other terminals by means of which the said coil may be connected in the desired circuit. The coil 2:: is held within the opening 23 by means of two thin sheets 25 and 26 of insulating material which are secured to the mounting 2! by rivets 21. The coil 24 is so constructed that the same has a central opening 28 therein which is rectangular in form and of an appreciable width as shown in Fig. 4. Said opening gives the coil 24 a core which consists principally of air and of the insulating material of the sheets 25 and 26 overlying the coil. Said coil thus has a core of non-magnetizable material.

The coil 24 is mounted for movement within an air gap 29 formed in a core structure 3|. The core structure 3i includes a U-shaped core member 32 having two spaced legs 33 and 34 and a connecting portion 35 at one end of each of said legs. The other ends 36 and 31 of the core member 32 form poles which have pole faces 38 and 39 extending outwardly therefrom and lying substantially in a common plane.

The core member 32 is supported in the following manner: Overlying the flange M of frame Ill is an angle member :56 which has a base 41 resting upon said flange and an upright leg 48 extending upwardly from said base. Both the base 57 and the flange it have elongated slots 49 in the same and through which bolts 5! extend. By means of this construction, the upright leg 48 of the angle member 46 may be moved toward and rom the upright I2 of frame Ill. The connecting portion 35 of the core member 32 lies against the portion 48 of the angle member 46 and is held legs ii i.

attached thereto by means of two screws 52. These screws extendthrough a bar 53 overlying the connecting portion 35 of the core member 32 and are threaded into the leg 43. The two legs 33 and 34 of the core member 32 have windings t and 55 mounted thereon which are so energized as to create a continuous magneto field directed out of one pole face. and into the other. The device operates in a manner. to be presently more fully described.

The air gap 29 lies between the two polefaces 3S and 39 and the face 4i of another core member 42. The core member 42 is in the form of a laminated bar and is imbedded in a block :43 .of-insulating material. This block overlies the upright i2 and is securedthereto by means of a number of screws 44 which pass freelyg-throughsaid uprightqand threaded into said block. Other screws threaded in the upright i2, engage the rear suriaceof the block 43'and serve to adjust the core member .42-with reference to the pole .faces 33 and 39 of the core member 32.

the magnetic-field caused by energization of coils 5 and 55 passes from one poleuface of core 32 across air gap 28 through bar 32 and backacross the air gap to the other, pole face, completing its path through core 32. When coil 24 isin its normal position, shown in Figs. 3and i, there is little magnetic linkagebetween the coil. and the fields established; acrossthe gaps, and such linkage a takes place .haveequalgand opposite effects on the coil. When, however, the coilis shifted to either side by swinging. the same on the-axis of the shaft 59,- the linkage-with one of the fields is increased while that:.with, the other, field decreases. 'flhe resultant eiiectivelinkage induces analternating voltageinthe pickup coil 26 which .is of one phase or the oppositephase, depending .on thedirection in which'the pickup coil is moved.

For displacement of the pickup coil usual to one thewidth of thepole facethe signal is. proportional tothe amount of displacement.

The actuating member has .a pendulum action when moved by a yieldable force. Tobring the-said member rapidly to restgafterithe same has been 'moVedJa damping device 5i is employed wh' n'isbest shown in FigsHZand j'llhisdevicecoinprises a core structure which, includes a bar 53 having anumber of vlegsflG-i andiii projecting outwardly therefrom. The bar 63 is rigidly securedto the block 43 of insulating material by means ofsc-rewsnot shown. Mounted on the legs it are windings Glwhichare connected in manner to be presently described. Operating ,in conjunction with the core structure G2 is ,an-

other core-structure 69 identical therewith. core structurehas a bar 69 and. legs. iii extending outwardlytherefrom and corresponding .to the Mounted onthese l gs are windings 12 which correspond with the windings ti. Other legs, similarto thelegsfiz' arealso provided for the core structureES, so thatair gaps '53 are formed betweenthelegs of the two core structures. In. the air, gaps 73 is movably positioned .an arcuate conductor "which is attachedto the ent line AC. having two conductorsfil provide a st produced in th prehended, however,

connected to the. conductor.

insulating mounting 2! of actuating member 20 by means of screws i5. These screws pass through an ear it on the said conductor and through a spacer Ti and are threaded into the mounting 2i. The conductor l4 travels in the various air gaps l3 and when the core members 62 and 68 are energized, set up eddy currents which retard the-movement of the actuating member 35 to which the said conductor is attached and rapidly bring said actuating member and the coil 24 to a stationary position. For the purpose of adjustment,.the.core structure 63 is mounted on the upright '53 by means of screws Si and 82 which function in the same manner as the screws 44 and 45 which ttach the block 43 to the upright Whileour;inventionhas many uses, the same is particularly adapted to be connectedin a system whereby a feeble control force may be converted into a su. tantial operating force. One suchsystem is 1 in Fig, i. In this system, energization is. from an alternating curr and 92 connected to the primary 9E oi a transformer Q4.

The transformer t4 has a first secondary winding -95 centertap .winding 33?.

d at and a second. secondary e secondary- 9? is connected by rose. s of conductors and with the two windingr of the control device proper. The coil 24 of this control device is connected by means ofconduetors ifii and ittwith a variable resistance 83. The conductor W2 is also grounded. Resistance 5 3?. has a tap M which is connected by means oi" a conductor -'\vith the grid Hit of a therro "nic tube Hit. The plate it-9 of this tube'is connected of ,a conductor ill with one side of a condo; ser 5 The conductor Hi is also connected toe resistance 1 i3 which is connected in series to a source or" voltage H4. This voltage is grounded asindicated at H5. The other side of the condenser i i2 is-connected. by means or" aconductor i with the grid 5 H of anotherthermionictube The conductor H9 connects the conductor 5 with a resistance H8 4 I bl which isv grounded. The conductor H5 has a branch ash which. ccnieetcdto the grid in of another thermionic tube so that the output from th tube iiii feeds to. both of tubes 28 and I23. lhe plate. of the tube IE9 is connected by means of a conductor 25 with one side of the transformer secondary The plate Hit of tube lit issimilarly connected by means of a conductor is? with the other side of secondary The cathodes of all cf'the tubes it i, and !23 are grounded andlmay be heated in any desirable manner. The tube it associated elements ,c oi amplification for the signals e coil It will be readily comthat additional stages may be einployed'if desired.

For utilizing 1e amp signal from the coil r 53E is ci'nployed. This motor .sifole type may consist of a and two wind u and 53 associ is at all times and 533 which are 86 and leading from the transformer secci y A condenser 12:? is con ected in the c cuit in series with the winding The win 3 2 is connected at one end by means of conductor E38 with center tap .353 of the secondar 95 of transformer 94. The other end of the winding I24 is grounded.

l-Il hi Winding 34 operates in a manner such that when the current through the conductor 138 changes phase by 180, the motor i3l reverses its direction of operation and when current in said conductor is zero, the motor stops.

The manner of connecting up the damping device GI is shown in Fig. 5. Each of the coils 61 is connected at one end to a common conductor l4! and at its other end to a common conductor I42. These conductors are in turn connected to the conductors M3 and M4 of a direct current line DC. One end of each of the windings I2 is similarly connected to a conductor I45 which is connected to the conductor M3 and the other ends of these windings are connected to a common conductor 146 which, in turn, is connected to the conductor I44 of the line DC. In this manner, direct current is supplied to the various windings 61 and 12, causing flux to flow in the core structures 62 and 68 through the air gaps 73. This flux passes through the conductor M, producing h eddy currents therein. These eddy currents produce a drag on the actuating members 29 which bring the coil 24 rapidly to a stationary position.

The operation of the invention is as follows: Assume that the shaft [9 is to be connected to a thermometer for indicating the temperature in a room and that the motor I3! is connected by suitable gearing or other transmission to the shaft of a damper controlling the operation of a heater for heating the room in which the thermometer is located. In such an association, 2. call for heat by the thermometer would swing the shaft l9 and move the coil 24 out of its normal position. The fluxes from the two pole faces 38 and 39 intercepted by the coil 24 would then be different and a voltage would be set up in the coil. This voltage would be amplified through the tube 10! and impressed upon the two tubes I and I23. A voltage would then be impressed upon the winding N4 of motor I31, which voltage would depend upon the phase of the voltage of coil 24 produced by shifting said coil from its normal position. Motor I3| would, of course, be connected in a manner such that rotation of the same as produced by shifting of the coil 24 in the direction specified would cause the damper to move in a direction to procure more heat. If the coil moved in the opposite direction, the phase of the voltage across the winding I34 would reverse and the motor would operate in the opposite direction.

The advantages of our invention are manifest. The device is particularly adapted to installations where a pivoted operating member is desired. Since the core of the actuating coil is of nonmagnetizable material, the back torque is negligible and the reluctance of the device remains the same for all positions of the actuating member. With our invention, a good zero signal is procured. The movable member comes back to stationary position in an exceedingly short time without affecting the sensitivity of the device.

Changes in the specific form of our invention, as herein described, may be made within the scope of what is claimed without departing from the spirit of our invention,

Having described our invention, what we claim as new and desire to protect by Letters Patent is:

1. In an electrical control device, a core structure including first and second core members of magnetizable material in near abutting relationship having spaced fixed air gaps defined therebetween by the extremities of said first core member in proximity with said second core member lying in the same plane. means for maintaining opposite alternating magnetic fields across said air gaps, a hollow inductor rectangular in cross-section mounted for movement transversely across said air gaps, the length of the hollow portion of the cross-section of said inductor being greater than the overall distance between the extremities of said first core member lying in the same plane, and means guiding said inductor for transverse movement to vary the portions of the field of one of said air gaps which traverses said inductor whereby an alternating voltage is induced in said inductor which is variable in phase and magnitude.

2. In a control device, a coil, a core structure of magnetic material including two core mem bers in near abutting relationship having an air gap therein for the reception of said coil, means for maintaining opposite alternating magnetic fields across said air gap, pivot means having its axis parallel with the direction of extent of said air gap for guiding said coil for swinging movement transversely of said air gap, from a neutral position of said coil, said coil encircling said air gap at said neutral position and having variable portions of said magnetic field in a particular direction traversing therein as said coil is moved from said neutral position in either direction.

3. In an electrical control device, a coil, a core structure of magnetizable material including two core members in near abutting relationship having a fixed air gap therein for the reception of said coil, means for maintaining equal and opposite alternating magnetic fields across said air gap, means for guiding said coil for movement transversely of said air gap from a neutral position in a plane at right angles to the direction of the extent of said air gap, said coil encircling said air gap in said neutral position, a planiform conductor carried by said coil and lying in a plane parallel to the plane of movement of said coil, and magnetic means associated with said conductor for dampening the movement of said coil.

4. In an electric control device, a magnetic core structure including a first and second core member in near abutting relationship, one of said core members having a pair of spaced pole pieces thereon projecting toward the other of said core members to define a pair of fixed air gaps spaced from each other, means for maintaining opposite alternating magnetic fields in said air gaps, a coil simultaneously encircling both of said air gaps in a normal position and being normally disposed in proximity to opposite edges of said air gaps with the central axis of said coil ex tending between said air gaps, and means for supporting said coil for movement in said air gaps and in a direction transversely thereof.

FRED P. STROTHER. BERT A. 0088.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,988,458 Minorsky Jan. 22, 1935 2,136,219 Scherbatskoy Nov. 8, 1938 FOREIGN PATENTS Number Country Date 473,563 Great Britain Oct. 15, 1937 

